1. Field of the Invention
The present invention relates to the precise measurement of physical objects and particularly to facilitating the maintenance, and thereby insuring the continued accuracy, of precision linear measuring instruments such as interferometers. More specifically, this invention is directed to guage fingers for use on precision measuring instruments and particularly to guage finger which include a field replaceable contact element which may be in the form of a jewel bearing. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
2. Description of the Prior Art
While not limited thereto in its utility, the present invention is particularly well suited for use as a gaging finger of a linear measurement interferometer. Such a measuring instrument is generally described in U.S. Pa. No. 4,509,858 and includes a probe, schematically indicated at 15, having a contact end 18 which is brought into engagement with the workpiece to be measured. In accordance with the prior art, the workpiece contacting member, i.e., the gaging finger, of a linear measurement instrument has customarily been constructed generally along the lines of gage arm 42 depicted in FIGS. 4 and 5 of U.S. Pat. No. 4,417,816. In the latter patent, the gage arm is provided with a pair of oppositely disposed tips or contact elements 44 and 46 one of which will be brought into abuttment with the workpiece during a measurement procedure, the tip which actually engages the workpiece being determined by whether an internal or external measurement of the workpiece is being made. The "tips" of the gage arm of previous linear measurement instruments have employed flat, cylindrical or spherical contact surfaces which were comprised of a wear resistant material such as diamond, ruby, carbide or hardened steel.
In order to maintain the accuracy of a linear measurment instrument, an interferometer for example, periodic replacement of the workpiece engaging elements has been required since these elements are subjected to wear as a result of their contact with the workpiece surface. Such replacement has often previously required replacement of the entire gaging finger subassembly, this being particularly true in the case of gaging fingers which could be employed to perform internal measurements. When the instrument is employed to make external measurements and employs spherical contacts, it has been common practice to replace the gage tip as a subassembly. In either event, in accordance with the prior art, the instrument operator was either required to have extra contact point or gaging finger subassemblies on hand or to remove the gaging finger from the measuring instrument and return it to the manufacturer for rework. The first option obviously requires that the instrument operator incur the added cost of having extra finger or contact point subassemblies on hand. The second option obviously imposes the significant disadvantage of rendering the measurement instrument unusable during time periods when the gaging fingers are being reworked.